Try this instead
missed a few , and " out
=SWITCH
(
LAST(Fields!Value.Value, "DataSet1") = 0, "White",
FIRST(Fields!Value.Value, "DataSet1") >= LAST(Fields!Value.Value, "DataSet1"), "Green",
(FIRST(Fields!Value.Value, "DataSet1") / LAST(Fields!Value.Value, "DataSet1")) >= 0.7, "Yellow",
(FIRST(Fields!Value.Value, "DataSet1") / LAST(Fields!Value.Value, "DataSet1")) < 0.7, "Red"
)